azure-pipelines-task-lib and isOutput setVariable

Some blog posts are insightful treatises on the future of web development, some are "here's how I solved my problem". This is most assuredly the latter.

I'm writing an custom pipelines task extension for Azure Pipelines. It's written with TypeScript and the azure-pipelines-task-lib.

The pipeline needs to output a variable. Azure Pipelines does that using the setvariable command combined with isOutput=true. This looks something like this: ##vso[task.setvariable variable=myOutputVar;isOutput=true]this is the value".

The bad news is that the lib doesn't presently support isOutput=true. Gosh it makes me sad. Hopefully in future it will be resolved. But what now?

For now we can hack ourselves a workaround:

import * as tl from 'azure-pipelines-task-lib/task';

import * as tcm from 'azure-pipelines-task-lib/taskcommand';

import * as os from 'os';

/**

* Sets a variable which will be output as well.

*

* @param name name of the variable to set

* @param val value to set

* @param secret whether variable is secret. Multi-line secrets are not allowed. Optional, defaults to false

* @returns void

*/

export function setOutputVariable(name: string, val: string, secret = false): void {

// use the implementation of setVariable to set all the internals,

// then subsequently set the output variable manually

tl.setVariable(name, val, secret);

const varValue = val || '';

// write the command

// see https://docs.microsoft.com/en-us/azure/devops/pipelines/process/variables?view=azure-devops&tabs=yaml%2Cbatch#set-a-multi-job-output-variable

_command(

'task.setvariable',

{ variable: name || '', isOutput: 'true', issecret: (secret || false).toString() },

varValue

);

}

const _outStream = process.stdout;

function _writeLine(str: string): void {

_outStream.write(str + os.EOL);

}

function _command(command: string, properties: any, message: string) {

const taskCmd = new tcm.TaskCommand(command, properties, message);

_writeLine(taskCmd.toString());

}

The above is effectively a wrapper for the existing setVariable. However, once it's called into the initial implementation, setOutputVariable then writes out the same variable once more, but this time bolting on isOutput=true.

Finally, I've raised a PR to see if isOutput can be added directly to the library. You can track progress on that here.